This invention relates to polarizing systems, and in particular, to a device utilizing a polarizer for eliminating undesirable radiation while permitting passage of desired radiation. While the invention is described in particular detail with respect to light ray projection in an aircraft flight simulator, those skilled in the art will recognize the wider adaptability of the invention disclosed hereinafter.
It is conventional to provide aircraft flight simulators which are detailed mock-ups of a particular aircraft for which training is being provided. That is to say, the flight deck or cockpit of a particular aircraft is recreated so that flight crews can fly the simulator prior to flying the actual aircraft. Generally, sound, motion, and visual sensory perception are provided during such simulated flight. Modern simulators provide physical sensations that closely approximate those experienced in actual flight. One of the more common simulation experiences for which training is provided is landing and take-off of the aircraft. Training in night and instrument landing approaches in particular are practiced, these being among the more difficult aircraft flight procedures. Commonly, the pilot of the simulator is provided with a CRT (cathode ray tube) display which corresponds to the window view of the pilot. That is, the view normally observable by the pilot of an aircraft is replaced, in the simulator, by an electronically generated display that closely resembles an actual airfield. The display changes in response to any simulator aircrat position change. Flight crews thus are able to acquaint themselves with the performance characteristics of a particular aircraft before ever actually flying the aircraft.
One particular simulator window design finding commercial acceptance has a CRT display device arranged so that the image electronically displayed on the CRT is projected to a beam splitter where it is reflected toward a mirror. The desired image is reflected by the mirror back through the beam splitter so that an observer in the simulator sees the mirror reflection. The particular system just described is advantageous because it affords a highly effective yet relatively low cost optical system for presentation of a desired scene.
As indicated, one of the training situations for which simulation training is provided involves night approaches to a landing field. In these situations, the initial view observed by the pilot may consist merely of light points in the field of view. As will be appreciated by those skilled in the art, the flight deck or cockpit of modern aircraft contains a multiplicity of illuminated dials. Prior to my invention, light waves generated by the illuminated dials passed through the simulator window and the beam splitter to the mirror, where they were reflected back through the beam splitter to the observer. For the purposes of this specification, the term "beam splitter" is intended to be an example of various materials that partially polarize radiation passage through the material. The reflected light confuses the window scene, and is both annoying and distracting to aircraft flight personnel in the simulator.
Circular polarizers are known in the art and often are used to eliminate reflected light. For example, it is known that a plane polarizer and a quarter wave retarder can be arranged to eliminate light originating on a first side of the polarizer so that light passing through the polarizer and retarder to a reflective surface from where it attempts to return back through the retarder and polarizer will be blocked by the polarizer. Such a system is diagrammatically illustrated in the drawings at FIG. 1, and labeled as prior art.
Circular polarizers, however, are not acceptable in the particular application described above because the optical system of the simulator utilizes a dielectric beam splitter as an integral part of the system for image generation. Dielectric beam splitters in general, reflect S plane wave components more than P plane wave components so that upon return to the circular polarizer, the reflected light is not merely a diametrically opposed polarization of the original polarization provided by the circular polarizer. Consequently, the circular polarizer permits some reflected light back through it, into the field of view of an observer of the window. As will be understood by practioners in the art, P plane wave components, or P polarized light is light having its electric vector polarized parallel to the plane of incidence of the light, while S plane wave components, or S polarized light, is light having its electric vector polarized perpendicular to the plane of incidence. The plane of incidence is defined as the plane containing both the normal to the beam splitter, at the point of incidence, and the incoming ray of light.
My invention eliminates the prior art difficulty with reflected light by utilizing an elliptical polarizer arranged properly with respect to the beam splitter. That is to say, total extinction of the reflected light is achieved by imparting an elliptical polarization to the light beam such that, when the beam is transmitted through the beam splitter, which may be considered an example of a variety of partially polarizing materials, and returned through that material, the beam becomes polarized with the same ellipticity but with orthogonal orientation. As described in greater detail hereinafter, the invention resides in part in the ability to easily define the proper elliptical polarizer for any beam splitter and the ability to easily calculate the orientation of components of the elliptical polarizer in any of a variety of embodiments.
My invention also provides a method for measurement of the ratio of P and S plane transmittance of a material when light is passed through partially polarizing material and reflected back through the same material.
One of the objects of this invention is to provide a device for eliminating reflected radiation transmitted through a partially polarizing material to a mirror and returning through the material, while allowing passage of that radiation making only a single pass through the material.
Another object of this invention is to provide a low cost method for measuring the ratio of P and S polarization transmittance through a material.
Another object of this invention is to provide an economical structure for eliminating undesired light when the undersired light passes and is reflected back through a partially polarizing material.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.